The purpose of this study is to determine the mechanism by which the lung accumulates large amounts of 1,2 dipalmitoyl-sn-glycerol-3-phosphorylcholine (DPPC), a major component of pulmonary surfactant. In vitro experiments will be performed on the continuous cell line A549, a model system for studying surfactant synthesis, to determine which reactions are important in DPPC synthesis and to determine the mechanism for the accumulation of DPPC in lamellar bodies. Similar studies will also be performed on primary cultures of mixed lung cells and type II alveolar cells. A second objective is to determine the step in the CDP-choline pathway that accounts for increased synthesis of phosphatidylcholine, particularly DPPC, in developing lungs. To this end primary cultures of mixed lung cells and type II alveolar cells will be prepared from lungs of rats (or rabbits) at various stages of prenatal development and the rates of the various reactions in the CDP-choline pathway, as well as the retailoring reactions, will be determined in vitro. Since the synthesis, degradation and storage of DPPC involves the interaction of a number of reactions, these studies will provide new information identifying those reactions which are important in the accumulation of DPPC in the lung.